Generally in using a door, it will be convenient if the door is moved lightly and fast when opening, but slowly when closing. It is also desirable that, when closing, a door is slowly fitted back without generating any impact after making a preliminary stopping.
The typical conventional door closers which are widely used are constituted such that a rack is elastically supported by a spring installed within the hydraulic chamber, the rack is meshed to a pinion, and a link is actuated by means of such mechanism. But in such conventional hydraulic door closers, the total inner space is used as the hydraulic chamber, and the pinion is positioned under the rack. This means that the force-receiving point deviates from the centre, and therefore, the door is hard to open, while the door, when released, quickly rushes back with a strong force due to the reacting force of the spring.
Further such conventional hydraulic door closers require the sealing of the opposite ends of the main body and the opposite sides of the pinion, thereby rendering the constitution more complicated. Such structure increases the possibility of the leaking of the hydraulic fluid. A further inconvenience is that, in order to keep the door at a certain opening angle, the bottom of the door has to be supported by means of a separate object. Also the main body of the closer is necessarily enlarged in order to acommodate the spring, thereby aggravating the external appearance and the commercial merit.
Further such conventional door closers use two arms which are connected by means of a hinge, and which are actuated in a folding type. Therefore all the force is imposed on the link mechanism, and consequently, friction and wear on the hinge is severe, and the arms are twisted or bent.
Thus the conventional door closers have problems both in the inner mechanism and on the external arms, and therefore, they have to undergo excessive operating loads together with frequent operating disorders.